9. Signals and Sampling Theory

Often there are times when you may want to examine how the power spectrum of a signal (in other words its frequency content) \emph{changes} over time. In speech acoustics for example, at certain frequencies, bands of energy called formants may be identified, and are associated with certain speech sounds like vowels and vowel transitions. It is thought that the neural systems for human speech recognition are tuned for identification of these formants.